Propelling charge (or prop charge as it is known) propulsion operates by generating a reaction force acting on the cross-sectional area of the aft end of a projectile. A typical prop charge is a powder or grain tamped in a combustion chamber. For a proper launch, the prop charge must be burned efficiently and at a steady, fast rate. In many applications, the projectile is launched from a tube which can be supported on a mount or by an individual.
At launch, the burning prop charge generates exhaust gases. Accordingly, handling of the exhaust gases is an ongoing concern. If exhaust gas exits the back end of the launch tube, disadvantages include the creation of a potentially lethal zone behind the launcher caused by the shock waves, the presence of turbulent hot toxic gases, the generation of considerable sound and pressure levels, and the discharge of flash and smoke. These disadvantages therefore generally prevent the use of such launchers in confined or closed spaces, or in covert operations.
In addition to the discharge of lethal exhaust gases, recoil forces are another concern in prop charge propulsion. To counter recoil forces, a countermass is required. The prop charge is typically sandwiched between the projectile to be fired out the front of the tube and a countermass to be discharged out the rear of the tube. The choice of countermass is an obvious concern because it endangers anything in its path. In general, the discharged countermass is inherently dangerous because it involves a solid or particle mass followed by or mixed with toxic and/or hot gases. Further, the noise, visual and/or thermal signature associated with the discharged countermass and gases can be detected thereby revealing the location of the launching man or crew.